Thousands of copies of the book by the renegade MI6 officer Richard Tomlinson, the Big Breach, were being distributed to bookshops yesterday as government lawyers conceded there was nothing they could do to stop it.

The paperback is being issued by Cutting Edge, a company linked to Mainstream Publishing, an independent firm based in Edinburgh. Bill Campbell, joint managing director, said yesterday the print run of 12,500 copies, for sale at £9.99, had almost sold out.

The Westminster bookshop Politico's sold 50 copies in half a day, said Iain Dale, its managing director. He was not entirely in favour of the book but, since it was available in Moscow and its contents had been published in national newspapers, its sale had become an issue of freedom of speech.

Whitehall lawyers have told publishers that the crown holds the copyright of the book and Mr Tomlinson signed an agreement to that effect in 1997. Mr Tomlinson says he signed under duress.

He has been paid an advance of about £28,000 by the Russian publisher of the hardback edition, but government lawyers will try to ensure he gets nothing from the UK publisher. Whitehall officials said yesterday they would not attempt to prevent the publisher or bookshops from making money from sales.

The book, which MI6 says is damaging, gives an account of Mr Tomlinson's operations and exploits in Russia, as well as the training and tradecraft of Britain's secret intelligence service. Mr Tomlinson has left Italy where he worked in a bar and is now living in Cannes in the south of France. Yesterday he insisted the book was not damaging, and added: "The government and country carries on."

When the government set up its promised special employment tribunal for former members of the security and intelligence agencies he would be the first to demand a hearing, he said.